In a semiconductor manufacturing process for manufacturing semiconductor devices, liquid crystal panels, LEDs or the like, a process gas is introduced into a process chamber which is being evacuated to perform various processes such as an etching process, a CVD process or the like. Further, the process chamber and exhaust apparatuses connected to the process chamber are cleaned periodically by supplying a cleaning gas thereto. Because exhaust gases such as the process gas, the cleaning gas or the like contain a silane-based gas, a halogen gas, a PFC gas or the like, such exhaust gases have negative effects on the human body and on the global environment such as global warming. Therefore, it is not preferable that these exhaust gases are emitted to the atmosphere as they are.
Accordingly, these exhaust gases are made harmless by the exhaust gas treatment apparatus provided at a downstream side of the vacuum pump, and the harmless exhaust gases are emitted to the atmosphere. In the exhaust gas treatment apparatus, in many cases, oxidation reaction treatment by combustion or application of heat from a heater is performed. In such combustion-type or heater-type exhaust gas treatment apparatus, when the exhaust gases containing silane (SiH4) are treated through the oxidation reaction, silica (SiO2) is produced. The produced silica is powdery, and adheres to an inner wall of a treatment chamber and becomes increasingly deposited. Therefore, it is necessary to remove periodically powdery product containing silica which has adhered to and has been deposited in the treatment chamber. Thus, a scraper is installed to scrape off the powdery product from the wall surface of the treatment chamber in the exhaust gas treatment apparatus. A circulating water tank is provided below the treatment chamber, and the powdery product scraped off by the scraper is deposited on the bottom of the circulating water tank.
Conventionally, in order to discharge powder deposited on the bottom of the circulating water tank, a bubbler is provided on the bottom of the circulating water tank and pressurized air is supplied to the bubbler, so that bubbling is performed in the circulating water tank to allow the powder to be floated and agitated, thereby automatically discharging the powder together with drainage water from the circulating water tank.
However, the bubbler tends to be clogged by the powder in structure at a nozzle portion for generating bubbles, and thus there is demand for a system which can discharge the powdery product accumulated on the bottom of the circulating water tank without using the bubbler.
Further, it is problematic that relatively small particles are floated and discharged by the bubbler, but large particles are not floated, thus being accumulated in the circulating water tank.